Belgium might yet become dark horses, but first they had to avoid an upset.

Substitutes Marouane Fellaini and Dries Mertens scored second-half goals as Group H favourites Belgium came from behind to defeat Algeria 2-1 on Tuesday in both teams' World Cup opener at the Estadio Mineirao in Belo Horizonte, Brazil.

Sofiane Feghouli had given Algeria a shock lead with a 25th-minute penalty before Belgium boss Marc Wilmots turned the game around with effective substitutions in the second half. Fellaini equalised in the 70th minute, and Mertens grabbed the winner 10 minutes later as the Red Devils got their World Cup campaign off to a winning—though bumpy—start.

Widely hailed as dark-horse candidates for glory in Brazil, by outlets such as BBC Sport, Bleacher Report and The Big Lead, Belgium boast a squad packed with top-level talent, including Manchester United's Fellaini, Chelsea playmaker Eden Hazard and Atletico Madrid goalkeeper Thibaut Courtois. But if the Red Devils are to make good on their promise, their stars will have to produce a more consistent performance as they continue group play.

And it might only become more difficult from here. After struggling to collect three points against outsiders Algeria, Belgium will now face potentially tricky matches against Russia and South Korea in their final group encounters.

Up next for Wilmots' side is Russia on Sunday. Algeria will play South Korea the same day.

Hassan Ammar/Associated Press

Dries Mertens blasts in the winner for Belgium.

Having come to the World Cup with so much promise, Belgium began the tournament with a forgettable first half. The Red Devils dominated possession and attempted to attack but were unable to break down Algeria's well-organised defence.

With Belgium struggling in the offensive third, Algeria won a penalty in the 23rd minute with their first real attack of the game. Feghouli won the spot-kick after being pulled down by Jan Vertonghen, and then converted it himself with a low shot down middle.

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Belgium were stunned into action but were unable to equalise before half-time, though Axel Witsel forced a save with a rasping shot from distance in the 34th minute. As B/R's Matt Jones noted, one issue for the Red Devils was a lack of width, due to having natural centre-backs playing on the defensive flanks:

Trailing 1-0 at the break, Belgium introduced Mertens ahead of the second half, in an attempt to liven up the attack. Chances quickly followed, with Witsel heading off target from a corner in the 50th minute, and substitute Divock Origi shooting straight at Rais M'Bolhi after being played in behind Algeria's defence.

Algeria maintained a sporadic threat as well, with Carl Medjani heading just off target from a 56th-minute corner.

But Belgium's refreshed attack was not to be denied for much longer as Wilmots' substitutions paid dividends with a pair of late goals.

Fellaini, who had replaced Mousa Dembele just five minutes earlier, brought the Red Devils level in the 70th minute. With his back to goal as Kevin de Bruyne's cross came in from the left, the big midfielder showed superb body control to flick his header in off the underside of the crossbar.

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Ten minutes later, Belgium went ahead. De Bruyne was involved again, making a key tackle to start a blistering counter into Algeria's half. Eden Hazard played the final pass across the edge of the box for Mertens, who blasted in high at the near post for a 2-1 lead.

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It was almost 3-1 in the 83rd minute as Fellaini placed another powerful header on target, but M'Bolhi made a fine save to keep Algeria in the match. In the end, though, it mattered little as Belgium held on for a hard-fought win.

Grades

Belgium Player Ratings

Starting XI

Half-Time

Full-Time

Thibaut Courtois

6

6

Toby Alderweireld

6

7

Jan Vertonghen

4

5

Daniel van Buyten

6

7

Vincent Kompany

6

6

Kevin de Bruyne

6

7

Axel Witsel

7

8

Nacer Chadli

5

N/A

Mousa Dembele

6

5

Eden Hazard

6

7

Romelu Lukaku

5

5

Substitutes

Half-Time

Full-Time

Dries Mertens (for Chadli, 46')

N/A

8

Divock Origi (for Lukaku, 58')

N/A

7

Marouane Fellaini (for Dembele, 65')

N/A

8

Ratings by B/R UK

Algeria Player Ratings

Starting XI

Half-Time

Full-Time

Rais M'Bolhi

7

7

Madjid Bougherra

7

7

Faouzi Ghoulam

7

6

Rafik Halliche

7

7

Mehdi Mostefa

6

5

Nabil Bentaleb

7

7

Carl Medjani

7

7

Riyad Mahrez

7

6

Sofiane Feghouli

8

7

Saphir Taider

6

5

El Arabi Soudani

6

5

Substitutes

Half-Time

Full-Time

Islam Slimani (for Soudani, 66')

N/A

5

Mehdi Lacen (for Mahrez, 72')

N/A

5

Nabil Ghilas (for Medjani, 84')

N/A

6

Ratings by B/R UK

Post-Match Reaction

Belgium goalscorer Marouane Fellaini, a second-half substitute, said coach Marc Wilmots' changes made the difference. Speaking to FIFA.com, he said:

Everyone can see that it was guys who came off the bench who made the difference today. That's always possible with this team anyway because you know that we have a lot of strength throughout the squad. It's not just about the first 11 with us. And although it was me and the other two today, there are others who stayed on the bench who can be big and important players for Belgium at this World Cup.

Wilmots said his substitutions "injected pace" into the game, telling FIFA.com:

The game was too slow in the first half, and we just weren’t able to find a way past a team that refused to play football. The substitutions I made injected a bit of pace, which changed the game after the break. The players seemed like beaten men in the dressing room, but I told them that I was sure that we would score eventually. The points are in the bag—we’ve still got a long way to go, but we showed our strength of character.

Algeria coach Vahid Halilhodzic expressed disappointment after his side narrowly missed out on the upset. He told FIFA.com:

I’m left with the disappointing feeling of having come close to achieving something great. We suffered a lot in the second half, allowing Belgium to impose themselves physically. The different level of experience was a key factor towards the end. The match came down to little things, really, as well as the talent of our opponents. Marouane Fellaini’s goal was a case in point, as he’s one of the world’s best headers of a ball. We weren’t far away from pulling off an upset. I’d talked about how effective the Belgians are at counter-attacking, and unfortunately that was confirmed on the pitch.